package lizhe.dummynode;

public class HasCycle {
    public boolean hasCycle(ListNode head) {

        if (head == null)
            return false;

        ListNode fast = head;
        ListNode slow = head;

        while (fast != null && fast.next != null) {
            fast = fast.next.next;
            slow = slow.next;
            if (fast == slow)
                return true;
        }

        return false;
    }
}
